A. Athens and Sparta is your answer
Athens and Sparta are city-states of Greece, which participated in the Persian Wars. Before hand, Athens and Sparta were rivals, and they fought constantly, with Sparta usually winning (because Athens was the city-state of knowledge, while Sparta was based on war) However, with the attack of Persia, the two worked together with other city-states, including Corinth for example, to fight the invaders. They were successful, and that is how modern Greece was kindof created
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